The present invention relates generally to plastics. More specifically, the present invention relates to connectors, and methods for making same, that are used for medical procedures.
It is known to mold plastics into various components and parts. These components can be used in a variety of industries, including the medical industry. Such components include connectors for connecting containers, that may include a fluid for a medical procedure, to another container, device, or to a patient. These connectors include luer connectors, spikes, ports, and the like.
By way of example, it is known to use plastic spikes in continuous ambulatory peritoneal dialysis (CAPD). CAPD is a method wherein the patient's peritoneal membrane is used as a dialysis membrane to eliminate metabolic waste from the body. This mode of dialysis, in contrast to hemodialysis and the like, allows for a more continuous removal of toxic waste, such as urea, while allowing the patient freedom of movement and a near normal lifestyle.
For a typical patient, approximately four times a day, a bag of peritoneal dialysis fluid is transferred to the patient's peritoneal cavity. After a defined dwell time, the solution is drained from the peritoneal cavity into a drainage bag. These transfers must all take place in a sterile manner.
To provide a flow path to the patient's peritoneal cavity, a catheter is placed in the patient, and a transfer set is coupled thereto. The transfer set, which thereby extends from, and provides fluid communication with, the patient, terminates in a spike. The spike allows the patient to access fluid from a peritoneal dialysis bag by spiking the bag through a port or spiking a tube set extending from the bag. In a similar manner, when it is time to drain the solution from the patient's peritonium, the patient uses the spike to access the drainage bag.
The transfer set is attached to the catheter by a healthcare practitioner using a specific medical procedure that requires the utmost sterile conditions. By extending the usable life of the transfer set, and thereby limiting the frequency of such procedures, additional convenience and improvement in the quality of life can be provided to the patient receiving CAPD. Presently, even extended wear transfer sets must be changed every four to six months.
To insure a sterile access pathway, the spike and port or luer connection is sterilized each time a connection is to be made. It is known to use UV radiation to sterilize the spike. One such device is the UV-Flash.TM. germicidal exchange device available from Baxter Healthcare Corp. The UV-Flash.TM. provides a disinfection and microbial reduction of the spike and bag port. This is accomplished by bombarding the spike and port with UV radiation.
Accordingly, the spike, because it is used for periods of up to six months, is exposed to a long term accumulation of UV radiation. This creates a tremendous burden on the material of construction for the connecting device. In this regard, the spike is the most effected of the components in the connection system by the UV radiation.
Polychlorotrifluoroethylene is typically used for constructing extended wear spikes. Polychlorotrifluoroethylene provides high UV radiation transparency that insures that the inner lumen of the spike receives a sufficient dose application. The inner lumen surface is the dialysis fluid pathway and therefore, it is essential that this surface be sterilized. An additional advantage of this material is that polychlorotrifluoroethylene compared to other plastics is quite resistant to radiation damage.
Despite these advantages that are provided by using polychlorotrifluoroethylene for the spike, these spikes are not entirely satisfactory in all situations. Polychlorotrifluoroethylene is semi-crystalline. It has a rather high melting point of approximately 220.degree. C. Accordingly, during manufacturing, very high processing temperatures are required to convert the material to a useful shape in a thermoplastic manner.
Additionally, the material's crystallization tendency is inversely proportionate to the molecular weight, or molar mass, of the material. Therefore, to obtain the desirable mechanical properties, it is necessary to use the highest molecular weight compositions possible. This is measured in the trade as the Zero Strength Time (ZST) which is determined by ASTM test D-1430. Typically, the zero strength time must be greater than five minutes at 250.degree. C. using ASTM D-1430.
On the other hand, however, material at such a high molecular weight is very difficult to induce to flow. This is because the viscosity of the polymer melt of such a material is exceedingly high. Accordingly, high ZST material cannot be injection molded into desirable shapes. Although lower ZST materials are injection moldable, these lower ZST materials do not have the desirable mechanical properties, and they tend to crystallize quite rapidly. Upon crystallizing, lower ZST materials turn opaque and therefore have near zero UV transmission properties, preventing the material from being used for a spike in CAPD applications.
A current method for producing extended wear spikes utilizing polychlorotrifluoroethylene is to first extrude a rod in a specialized, corrosion resistant extruder. The rod is then converted to the desired shape by precision machining.
This method of fabrication has several disadvantages. In the first instance, it is a slow extrusion process of what is a rather large rod. Heat removal in the process is not very rapid. This leads to slower cooling and greater crystallinity, i.e., a more opaque material.
Additionally, the machining process, even if the tools which are used are frequently sharpened, creates numerous machining marks along the tool path on the spike. These machining marks on the spike can likewise create optical opacity, leading to a greater absorption of UV radiation by the material. This can result in subsequent radiation damage.
Moreover, these machine marks are typically microscopic grooves which tend to act as stress concentrators at the bottom of the grooves. The combined mechanical defects from the machining grooves in conjunction with the added radiation absorption, can lead to premature failures of the spike when subjected to repeated stress during the dialysis exchange process.
There is, therefore, a need for an improved method of manufacturing connectors for use in medical procedures that are constructed at least in part from a polychlorotrifluoroethylene material.